To examine the influence of age and the menopause on bone loss we studied 178 healthy women, aged 29-78 yr. Bone mass was measured at 2 forearm sites, in the total spine, in the lumbar spine, and in the whole body by single and dual photon absorptiometry. Women of the same age but different menopausal status had significantly different bone masses, whereas a 5-yr difference in age had no effect on bone mass in women with the same menopausal status. At the menopause the hormone changes (low serum estrogen and high serum gonadotropin levels) occurred simultaneously with the appearance of biochemical indices of increased bone turnover. Neither biochemical values nor bone measurements indicated significant bone loss before the menopause. We conclude that the menopause has a greater effect on bone loss than does chronological age.